1. Related Applications
This application is related to U.S. Ser. No. 909,332, titled SHIFT CONTROL METHOD/SYSTEM filed the same day, Jul. 6, 1992 and assigned to the same assignee, EATON CORPORATION, as this application.
2. Field of Invention
This invention relates to control methods and systems for controlling the shifting of at least partially automated vehicular mechanical transmission systems. In particular, the present invention relates to shift control methods/systems for automated mechanical transmissions wherein the likelihood of acceptably completing a selected upshift are evaluated in view of existing vehicle operating conditions and only acceptably completable shifts are initiated. An acceptably completable upshift is an upshift into a target ratio wherein, under existing vehicle operating conditions, the maximum available engine torque will cause at least a predetermined minimum vehicle acceleration.
3. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles, such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, transmission shaft speeds, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmissions utilizing electronic, hydraulic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, the disclosures of which are hereby incorporated by reference.
Semi-automatic transmission systems utilizing electronic control units which sense engine fueling, throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior art. Examples of such semi-automatic mechanical transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
Another type of partially automated transmission system utilizes a semi-automatic shift implementation system/method for a mechanical transmission system for use in vehicles having a manually only controlled engine throttle means and/or a manually only controlled master clutch. The system usually has at least one mode of operation wherein the shifts to be semi-automatically implemented are automatically preselected and includes a control/display panel or console for operator selection of a ratio change or operation in the automatic preselection mode and indication of automatic preselection of upshifts, downshifts or shifts into neutral. An electronic control unit (ECU) is provided for receiving input signals indicative of transmission input and output shaft speeds and for processing same in accordance with predetermined logic rules to determine (i) if synchronous conditions exist, and (ii) in the automatic preselection mode, if an upshift or downshift from the currently engaged ratio is required and to issue command output signals to a transmission actuator for shifting the transmission in accordance with the command output signals.
Under certain conditions, preselection and/or implementation of an automatically preselected shift is prohibited to prevent unexpected and/or undesirable shifts. Preferably, the operator is provided with means, such as manual depression of the clutch pedal, to release the shift prohibiting means. Conditions at which implementation of automatically preselected shifts should be prohibited may include relatively high or relatively low vehicle speed, operation of the vehicle brakes and/or retarder, and/or the fuel throttle in the idle position.
The control/display device will display the selected but not yet implemented shift as well as the current status of the transmission, and, preferably will also allow the operator to manually select/preselect a shift into a higher ratio, a lower ratio or into neutral. Preferably, the control device will also allow a manually or an automatically preselected shift to be cancelled.
Transmission systems of this general type may be seen by reference to U.S. Pat. Nos. 5,050,079; 5,053,959; 5,053,961; 5,053,962; 5,063,511; 5,081,588; 5,089,962; and 5,089,965, the disclosures of all of which are hereby incorporated by reference.
While the above-described automatic, semi-automatic and/or partial automatic shift implementation type vehicular mechanical transmission systems are well suited for their intended applications, they are not totally satisfactory as they will occasionally initiate an attempted shift, which, due to vehicle operating conditions, should not be completed. This is especially a concern for upshifts of automated mechanical transmission systems when the vehicle is operating against a particularly great resistance and the engine, in the target ratio is unable to accelerate or maintain vehicle velocity which will result in undesirable "hunting" as the transmission undergoes cycles of upshifts followed by almost immediate downshifts.